From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: why the sigma of symmetrical svd for a real symmetric matrix is negative?
Date: Thu, 27 Dec 2012 04:39:09 +0000 (UTC)
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"Rick" wrote in message <kbgbi5$g5n$>...
>  as we know,  for a real symmetric matrix A, A, there exists a singular value decomposition as A=USU',  and S should be a rectangular diagonal matrix with nonnegative real numbers on the diagonal. But when I use the command schur(),
> it seems that S appears negative real numbers on the diagonal as the following. Is there any problem?
 - - - - - - - - - -
  Unless your A matrix is positive definite there is no reason its singular value and schur decompositions should be the same, and the A you have defined is certainly not positive definite.  In fact all its eigenvalues are negative.  Check the Wikipedia site:

Roger Stafford